Palladium and Platinum: Uses light sensitive iron salts to produce an image on a plain paper, then replaces the iron with microscopic particles of the precious metals platinum or palladium. The metal is embedded into the paper fibers which results in a print with a three dimensional feeling as though the viewer could actually touch the objects in the photograph. The process responds to a great range of light and can interpret a scene with deepest shadows and most brilliant highlights. Good prints can be made from negatives so dense that by modern standards they are considered “bulletproof”. The tone of the print can be adjusted from cool blue-gray to warm brown by using varying mixtures of platinum and palladium. An oxidizer such as hydrogen peroxide is used to control contrast.
Platinum and palladium are precious metals like gold, and like gold have extreme permanence. Thus the prints are as permanent as the paper they are printed on. The highest quality paper must be used. I use a high quality 100% cotton paper which is designed for archival legal documents. Every cotton fiber paper has slightly different trace chemicals in it which results in variations in image color from paper to paper when used for platinum and palladium printing.
In the 19th and early 20th centuries photographers could buy paper already coated with platinum or palladium, however the modern photographer must have some knowledge of chemistry and prepare the chemicals in the darkroom. The light sensitive ferric oxalate is most responsive to ultraviolet light so that direct sun or florescent blacklights must be used, and only contact prints can be made. Although a difficult process, difficulty does not make up for an image lacking in imagination.